If you travel at a constant speed, you follow this formula:
[tex] s = vt [/tex]
where s is the space traveled, v is the speed and t is the time passed. Knowing the speed and the desired space, we can solve the equation for the time:
[tex] t = \dfrac{s}{v} [/tex]
Plug your values:
[tex] t = \dfrac{30}{45} = \dfrac{2}{3} [/tex]
And two-thirds of an hour are 40 minutes.
To convert his speed in miles per minutes, you only need to use that one hour is composed of 60 minutes:
[tex] \dfrac{45 \text{ miles}}{1\text{ hour}} = \dfrac{45 \text{ miles}}{60\text{ minutes}} = \dfrac{3 \text{ miles}}{4 \text{ minutes}} = 0.75 [/tex] miles per minute
